One of the first inklings that chemistry has an underlying pattern was the discovery, early in the 19th century, of lithium, sodium and potassium - known collectively as the alkali metals. Though different from each other they have strangely similar properties. This was one of the observations that led a German chemist called Johann Dobereiner to wonder if all chemical elements came in families.
It took decades to tease out the truth of Dobereiner's conjecture, and thus to construct the periodic table - in which the alkali metals form the first column. And it took decades more to explain why the table works (it is to do with the way electrons organise themselves in orbit around atomic nuclei). But it is a fitting tribute to Dobereiner's insight that, if all goes well, some time in the next few months will bring the creation of a new alkali metal, element number 119, by his countrymen Christoph Dullmann of the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt. With that addition the table will do something which has never happened before. It will grow a new row.
An element's atomic number is the number of protons in its nucleus. These, despite being mutually repulsive because they are positively charged, are held together by a phenomenon called the strong nuclear force. Some of the force is also supplied by neutrons, which outnumber protons in most nuclei and have no electric charge. If, however, there are too many or too few neutrons in a nucleus, that nucleus becomes unstable - in other words, it is radio active. And the vagaries of quantum physics mean that ゛too many゛ and ゛too few゛ sometimes overlap, and there is thus no stable isotope (or variant, with fewer or more neutrons) of a particular element.
This happens at two places - islands of instability, if you like - in the middle of the table. As a result technetium, element number 43, and promethium, 61, are always radioactive (and are not found naturally in detectable quantities). Further down the table, where nuclei get heavier and elements less familiar, instability happens more and more often. No element heavier than lead (number 82) has a stable isotope, and above number 92 (uranium) lifetimes are so short that these substances are almost non-existent in nature. Such゛transuranic゛element can, however, be made artificially by the fusion of lighter ones. And that is precisely what Dr Dullmann intends to do in the case of element 119, by firing titanium atoms (number 22) at those of berkelium (97) and hoping some of them merge.
Making a new element is tricky. The titanium atoms must be travelling fast enough in GSI's particle accelerator to overcome the repulsion between their protons and those of the berkelium, yet slowly enough to avoid ripping the newly formed atom of element 119 apart before it has had time to settle down. With the right mix, though, Dr Dullmann is confident that one or two atoms of 119 will be created over the course of the next few months, and will hang around long enough to be detected.
That will be a feather in GSI's cap in its friendly competition with the Lawrence Berkeley National Laboratory, in California (after which berkelium is named) and the Joint Institute for Nuclear Research in Dubna, Russia (after which dubnium, number 105, is named). Number 110 is named darmstadtium, and these three laboratories are, between them, responsible for the creation of all the transuranics found so far - most notably plutonium, which was used to blow up Nagasaki in 1945 and thus end the second world war.
